1. Field of the Invention
The present invention relates to hydrodynamic power transmission units in which the torque of a rotating drive shaft is transmitted to a shaft to be driven by a drive fluid.
2. The Prior Art
Hydrodynamic power transmission units are well known elements in all types of transportation vehicles, including automobiles, trucks, buses, airplanes, etc. Also known as fluid clutches, these units can be, for example, connected to drive the cooling fan of an air-cooled internal combustion engine (e.g. a diesel engine) at a controlled speed based on the operating characteristics of the engine. As shown in German Pat. No. 921,181, the drive fluid can be injected in metered quantities from a storage container into the clutch as required. However, since the amount of drive fluid which is in contact with the operating parts of the clutch is critical, it is necessary to prevent any lubricating oil which may be used in the bearings of the clutch from mixing with the drive fluid. Thus, most clutches are made with bearings which do not require the use of lubricating oils, such as roller bearings or needle bearings. But these types of bearings are easily contaminated and not adequately wear resistant, as well as quite expensive. And clutches made with such bearings tend to be noisy.
It is thus an object of the present invention to provide a hydrodynamic power transmission unit which can be made with readily available, low cost and highly resistant bearings.
It is also an object of the present invention to provide a low noise hydrodynamic power transmission unit in which lubricating oil is supplied to the bearings therein separately from the supply of drive fluid and in which the spent lubricating oil is removed from the bearings in a way that intermixing with the drive fluid in the clutch is prevented.
It is furthermore an object of the present invention to provide a hydrodynamic power transmission unit in which the same fluid can be used as both the drive fluid and the lubricating oil for the bearings.